Dry kiln and the art of kiln drying



Jgne so, 1942.

J. F. COBB 2,288,154

DRY KILN AND THE ART OF KILN DRYING Filed Jan. 10, less 2 Sheet s-Sheet 1 lnvenfon June 30, 1942. J, F, c095 2,288,154

DRY KILN AND THE ART OF KILN DRYING Filed Jan. 10. 1958 v 2 Sheets-Sh eet 2 gw w em bodiment,

Patented June 30, 1942 umrso srATEs; PATENT series DRY KEN AND THE ART OF KIL'N BRYENG James'Foriest Cobb, Portland, brag assignor to The Moore Dry Kiln -Company of Oregon, a

corporation Application January 10, 1938, Serial No. 184,284 9 clai s. (an. 34-26) a'more economical and more stable means for v quantity drying of lower grade lumber.

Another object of my invention is to provide a novel dryer means for eifecting more economical handling, more uniform drying and better quality drying than can be accomplished in ordinary dryers.

In progressive kilns now in use,'loads of material to be dried are put progressively into the kiln at intervals, one behind the other, On the same track so that dryer lumber is at the dry end and greener lumber is at the green end. The temperature in the kiln increases from the green end to the dry end and the humidity decreases accordingly. Multiple track charge kilns are also in use, and in these the temperature is plurality of parallel tracks, and of circulating av common drying atmosphere across the loads, the common atmosphere having substantially the same entering air temperature throughout the entire dryer and throughout the drying period. This method reduces steam consumption, reduces the cost of drying lumber such as the common grades which are dried in quantity, reduces handling costs through the dryer, and stabilizes the drying conditions and insures high quality of the kiln dried stock.

What constitutes my invention will-be more particularly pointed out in a detailed description which follows and succinctly defined in the appended claims.

In the accompanying drawings wherein my invention is.illustrated in preferred form of em- Figure I illustrates in transverse vertical cross section one form of embodiment .of my dryer.

Figure 11 is a longitudinal vertical section at IIII of Figure HI.

Figure III is a plan view-of Figures I and II.

Figure IV is a transverse vertical cross section of another form of embodiment of my dryer.

Figure 'v is a verticallongitudinal section of V-V of Figure VI.

Figure VI is a plan view of Figures IV and V.

Referring to the numerals onthe drawings in each figure thereof where they appear, I indicates the opposite side walls of the kiln, 2 the floor, 3 the roof and d the end walls defining a closed chamber and constituting the outside walls of the kiln. Said walls may be of any suitable material and construction and combined in any manner preferred so as to confine within the enclosed chamber the gaseous circulatory medi- ,um with the heat and moisture which are sup= plied to it.

The end walls t or at least one of them are preferably made to include some means of door 5 whereby the material to be dried may be conveniently introduced into the kiln and withdrawn from it.

Extending lengthwise through the dryer are a series of tracks or rails 5 which are supported on the floor iresting on the ground as in Figure I or at suitable intervals within the kiln at a desired elevation above the floor 2 by the cross beams I in Figure IV. Loads It of material to be dried are serially charged on the tracks. One track is loaded ata time and at periodic intervals of one day, for example, and when the track is emptied of dry stock it is reloaded with green stock so that the several tracks hold stock loads of difierentdegrees of dryness.

The tracks are designed to support and carry wheeled trucks 8 which may be of any usual form I preferred and which are united in pairs, prefer heating coils 3!, 32 and 33 between the stock loads and a row of fans it rotated by individual reversible gear motors l5, suitably wired to a source of electrical power, for circulating the atmosphere across the series'of stock loads it and recirculating the air above the loads through the recirculating space 55. Other arrangements of fans may be used as, for example, the arrangement illustrated in Patent No. 1,955,374.

Ifpreferably employ a substantially uniform temperature and humidity of the entering air throughout the' entire dryer. 1 preferably employtemperature and humidity recorder controllers 25 similar to that illustrated in Patent No.

the atmosphere drops to 136.

1,624,887; with a thermostatic bulb 29 in the kiln and a diaphragm valve 21 controlling the amount of steam supplied to the heating coils 28 and 30 through the pipe 24. The heating coils 3|, 32 and 33 between the loads supported by posts ll maybe supplied likewise to maintain the uniform temperature desired. Additional pipe is employed in the coils 26 and 30 of Figure IV to heat the incomingjresh air, depending upon the direction of air circulation. Each coil may be separately controlled if desired.

I preferably provide means for intake of fresh air into the kiln. For example, ,on two sides of the fan partition l6 illustrated in Figure I,

are ventilating means as controllable air intake ports 2| and ventilators 20 joined by the rod 69 for intake and outlet respectively of atmosphere to and from the kiln when the circulation is moving in the direction of the arrows. Fresh air may be taken in on the suction side of the fans through the portsZl of the ducts '23 and atmosphere may be exhausted from the kiln through the ports 20 of the duct 22. When cir-- cu'lation in the kiln is reversed, these ports are reversed in function. These may be in the side walls as doors 36 and 31 illustrated in Figures IV and VI or other usual ventilator means may be employed. By increasing 'theventilation of the kiln the amount of recirculation would be reduced, depending upon the amount of relative humidity desired. a

A common drying atmosphere is circulated transversely through the sticker spaces l3 across the several loads Ill on adjacent tracks so that air passing across a recently charged row of green loads will pass across heating coils .and'

then across the corresponding stockloads seriatim of different degrees of dryness on, the other After the atmosphereters each row of stock loads and this is the usual procedure. For example, considering Figure I.

the atmosphere enters the first row of stock loads 7 on the right of the fans at a temperature of 140. In passing across the first row of loads which may be, for example, one-quarter dry, the temperature drops to 134. The atmosphere is reheated by the heating coil 33 to 140. In passing across the second row of loads which are, for

example, about half dry. the temperature of The atmosphere is then reheated by the heating coils 30 and 26 in the space above the loads to 140. In passing across the third row of loads which are, for example, three-fourths dry, the temperature of the atmosphere drops to 138. In passing across the heating coils 3|, the temperature is again heated to 140. .In passing across the fourth row of loads, which are, for example, the greenest loads last placed into the kiln, the temperature drop may be to 132. The air in passing through the heating pipes 32 is then reheated again to 140 and is ready to pass across the first load again. When automatic heat control between each row is used for individual coils, such a temperature schedule may be automatic.

the second row of loads the wet bulb temperature w remains at 130%", and in passing across the heating coils 30 and 26 the' wet bulb temperature may rise to 131%. In passing across the third row of loads the wet bulb temperature remains the same. In passing across the heating coil 3|, the'wet bulb may be increased to 131 2 In passing across the fourth or greenest row of loads the wet bulb remains the same. In passing across the heating coils 32, the wet bulb tends to be raised to- 132 At this point the wet bulb controller which actuates the ventilators or in some cases of manual control, the operator lets in sufficient amount of fresh air and lets out a suflicient amount of kiln atmosphere so that the atmosphere is reconditioned insofar as the wet bulb temperature is concerned and the wet bulb temperature is again brought to 130.

The dry bulb temperature of the atmosphere can be controlled as it enters each row of loads to maintain the same humidity of the atmosphere entering each row by setting up the dry bulb temperature to give a desired humidity, or

the humidity may be allowed to raise as the air passes across successive loads. My invention contemplates the variation of temperature and humidity normally occurring as the atmosphere circulates across the series of rows of loads, which vary in degree of dryness, the gradual increase of the wet bulb temperature being a factor in heating up the green stock loads on the track filled on a particular day, more quickly than if all of the tracks were charged with rows atone time, which is the usual method.

and VI I employ a series of reversible rotary' fans 4| operatively mounted on a longitudinal shaft 42 and preferably rotated at the same speed by a suitable reversible motor 43 and drive. In Figure VI the shaft 42 rotates in bearings 44 supported bythe bearing stands 46 mounted on the intermediate floor 45. Transverse air circulation is effected by means of a zigzag fan duct wall comprising walls 41, 48, 49 and 50 extending substantially from endto end of the kiln in a zigzag direction as illustrated in plan in Figure VI.

nately disposed compartments formed by the substantially parallel walls 48 and 49, the diagonal walls 50, and the apertured wall 41. Each of the walls 48, 49 and 50 is so imperforate and each of the walls 41 is provided with an aperture of suitable dimensions to accommodate within it one of the series of rotary fans 4|. The walls 41, 48, 49 and 50 are united on adacent edges to form the compartments on opposite sides of The zigzag effect of the said well isachieved by the formation of a series of alter-' ."box 38 according to well known practice.

' I preferably provide heating means 26 and 30 the result is in the assemblage, to impart to the wall so constituted through its entire length what v is designated as a zigzag wall or effect.

The angle at which the walls 50 meet the walls 41 and 48 as shown in Figure VI is an obtuse angle on the same side. but it is obvious that the angle may be varied if desired as in some instances it may be. -Each' of the wallslast named rests on the intermediate-floor 45 of the I prefer to use a series of right hand. fans-at one end of the kiln and a series of left hand fans at the opposite end of each fan system,the zig zag wall being reversed in .direction at a medial ortion of the kiln as shown in Figure VI. 'In the intermediate compartment where right and left hand fans face each other, two fans will blow against each other in counteracting currents in one direction of air circulation and withdraw atmosphere from the 'same' compartment in the reverse direction of circulation.

In the zigzag assemblage, the walls 41, 48, *49 and 50 extend upward and connect with the partition 5| and its extension 52 the whole of which makes substantial closure with the top corner of the adjacent stock loads substantially the full length of the kiln. The assemblage of fan ducts thus forms a continuous partition through which the plurality of fans 4! circulate the kiln atmosphere. By employing two such cooperating fan duct systems, one at each side of the dryer as illustrated in Figure VI, one sucking air one side of the stock loads and the other blowing air from the opposite side of the dryer, one continuous circuit of transverse air circulation is effected across the stock loads onthe plurality of tracks.

A humidifying means is provided by the steam spray pipe 60 which is preferably automatically controlled by any well known means, such as. for example, a wet and dry bulb controller employing a'wet bulb 39 which operates a dia-, phragm valve" on the spray line 60 by means of air pressure from a source not illustrated. The

wet bulb 39is equipped with a, suitable water adjacent to each fan system for .heating the fresh air taken into the kiln by admixture with the recirculated air prior to its passage through the fans, the heating systems may 'be divided at the two ends of the kiln where the heatin systems exceed 50 feet in length.

In addition to the heating system mentioned above, I preferably provide heating means 3|, 32 and 33 between the stock loads to recondition the atmosphere after it has passed across one load and before it passes across another load in either direction of air circulation.-

I also preferably provide ventilating means shown in Figure'IV for the outlet of moist air air. The'controllable doors 36 in, sections on the suction side andthe controllable door 31 on the pressure side are reversible in function upon reversal of the air circulation and may be of sufiicient size when fully open to eliminate re circulation of air in the dryer. The doors are preferably automatically operated by motor levers 66 connected to them by chains 61 by means of compressed air in the pipe 68' from a source not shown. Whenfthe wet bulb falls below the set point, the vents 31 and air ports 38 are closed automatically. They likewise will 'open when the wet bulb temperature rises up to the setwet 5 bulb temperature. The vents as well as the humidifying sprays are operated by the controller depending upon the setting of the wet bulb tem perature. In the dryer illustrated in Figure I,

' I preferably Eondition the incoming fresh air bel0 fore it passes across the stock loads.

Considering that both fan systems are reversible, it is intended that the air shall be circulated in one direction by both systems for a period of time, for example, twelve hours, and air cirlo culatcd in the opposite direction across the loads for a similar period. The two fan systems mutually cooperate to eiTect uniform air circula tion across the adjacent stock loads successively on the several tracks. The loads may have voids go between their ends and if only {one fan system is used there is more short circuiting and less uniform circulation across the stock. The .two

fan systems, wit the stock loads all between them, effect uniform circulation and uniform 5 drying. The discharge of air from the fan sys tem is in jets of varying direction while'the suction of the ,fans is uniform and when two fan systems are used, one blowing and one sucking,

the circulation and drying are uniform. The reversal of air circulation also eliminates the ill effects of jets from the blowing fans as the series of blowing fans becomes a series of sucking fans upon reversal.

Suitable baflles 52 and 53 are provided to direct the air across the loads instead of allowing it to pass around them.

I preferably provide dual dry bulbs on each of the dry bulb tube systems of the controller with one bulb thereof on each side of the heatw'ing system to give control of the air entering the stock load in either direction of transverse air circulation. Two dry'bulbs, for example, 29

and 29-A, are connectedby capillary tubes 28 and 28A, and capillary 34 to one actuating element such as a helical coil IQ of the instrument.

See Patent No. 1,624,887. When dual dry bulbs are used, the bulb in-the hottest atmosphere, that having passed across the heating coil No. '30 in Figure IV, actuates the helical coil of the controller through effecting the higher vapor pressure therein.

The operation of my dryer isas follows:

A row of loads is placed on one track spref erably to fill'it substantially from doorto door 55 of the dryer and the dryer is ready for starting A common drying atmosphere its operation. having substantially the same temperature is circulated transversely across the loads. Later, for example, after twelve hours, a second track on is charged in a similar manner and the air is circulated across the two rows of loads. Similarly, after an. equivalent interval of time, a third track is charged 'with stock to be dried, of the same, or different kind, thickness and 1%.; moisture content. Similarly, after an equivalent from the dryer and for the intake of fresh interval a fourth track is charged. They are also serially recharged, usually in the same order, at regular intervals, for example, of twelve hours, twenty-four hours or thirty-six hours,-as one row 0 ofloads becomes sufllciently dry. The temperature Z the dryer and thattrackls'recharged with new material to be dried. For example. in a four track dryer the time schedule or the interval.

between the charging of different tracks is usually one-fourth of the dry ng P riod.

In the ordinary progressive dryer 'wet stock is put in at one end and it is progressed through the dryer in stages, the wetter stock following the stock-ahead of it and the temperature and humidity being changed as drying progresses. It is not possible to remove any of the stock except that at each door without discharging the entire kiln. Each time a load of stock is put into a progressive kiln all the loads must be moved in the kiln, which involves considerable labor. In my dryer the stock on any one track is removed .and replaced at regular intervals and only the row of loads put in or removed are handled. The other loads are not disturbed. This reduces the cost of handling the stock loads in my dryer. Also in my dryer a common atmosphere of uniform temperature is circulated across the loads of each track of varying moisture contentand stages of dryness.

The coils between the loads may be automatically controlled, if desired, to maintain a predetermined dry bulb temperature of the atmosphere after it has passed across the loads on one track and before it passesaeross the loads on the adjacent track. a

It is understood that this invention is not limited to the exact design and form illustrated and described. Modifications of the methods and structures herein described and mechanical equivalents are self-evident to those skilled in the art; therefore, it is to be understood that the invention includes within its scope whatever changes fairly come within either the terms or the spirit of the appended claims.

Having described my invention, what I claim is:

1. The method of kiln drying lumber which consists of serially charging into an enclosure air permeable stock loads of lumber in spaced parallel rows on tracks, one row at a time at substantially regular time intervals, so that each row of stock loads has been dried a diiferent amount from the other rows, circulating a common atmosphere through the rows of loads laterally from one side of the kiln to the other and in part back to the first mentioned side in recirculation, reconditioning the atmosphere between each row and replacing each row when it is dry with a green row.

2. The method of kiln drying lumber which consists of serially charging into an enclosure lumber. in spaced parallel rows of air permeable stock loads on tracks, one row at a time at substantially regular time intervals, so that each row of stock loads has been dried a different amount from the "other rows, circulating a common atmosphere through all ofthe rows seriatim and reconditioning the atmosphere between each row of loads to maintain a substantially constant temperature of kiln atmosphere which enters a stock load, and replacing each row when it is dry with a green row.

3. The method of kiln drying lumber which consists of serially-charging into an enclosure lumber in spaced parallel rows of air permeable stock loads on tracks, one row at a time at substantially regular time intervals, so that -each loads and comprising function when the fans I on each side of the fans,

g the other bulb being on row of stock loads has been dried at different amount from the other rows, circulating a common kiln atmosphere through all of the rows seriatim, reconditioning the atmosphere between stantially regular time intervals, so that each row of stock loads has been dried a different amount from the other row, taking in outside atmosphere, mixing-it with kiln atmosphere and circulating the mixture through the rows seriatim, reconditioning the atmosphere between each row of loads to maintain a substantially constant temperature of kiln atmosphere whichenters a stock load, venting a portion of the atmosphere after it has passed across all the rows of loads, and replacing each row when it is dry with a green row.

5. The method of kiln drying lumber, which consists of serially charging into an enclosure, lumber in spaced parallel rows of air permeable stock loads on tracks, one row at a time at substantially regular time intervals, so that each row of stock loads has been amount from the other row, taking in outside atmosphere, and circulating, it through the rows seriatim, reconditioning the atmosphere between each row of loads to maintain a substantially constant temperature of kiln atmosphere which enters a stock load, venting said atmosphere after it has passed across all the rows of loads, and replacing each rowwhen green row.

6.. In a multiple track dryer, a housing having within it a plurality of spaced tracks for the accommodation of end piled rows of air permeable stock loads thereon, a recirculation passageway having heating means therein, heating means between adjacent rows of stock loads, air circulating means between two of the rows of stock a plurality of reversible fans for recirculating. a common drying atmosphere across all of said rows of loads, and through said recirculation passageway and across the heating means there a ventilator and an air port for' each of said fans, said ventilator and air'port having conduits extending through the dryer housing to the opposite sides of said fans and adjacent thereto in operative communica tion with them, said fans being reversible. in are reversed, heating and the adjacent load whereby incoming fresh air is heated before passing across the loads in each direction of circulation, and a controller for one of said last named heating means, said controller having dual dry bulbs, one of said bulbs being on one side of said heating means, and the opposite side thereof.

'7. The method of drying which consists of serially-charging into an enclosure a series of rows of air permeable stock loads of material to be dried in spaced relationship, one row at a time at substantially regular time intervals so that each row of stock loads has been dried a different amount from the other rows, of recirculating a drying atmosphere across all of the rows of loads, of venting a. portion of the circulating atmosphere and replacing-it with fresh air, of conditioning the common atmosphere as it means between the fans dried a different it is dry witha stock load and a air, of conditioning passes from onerow of loads to another in recirculation to maintain a substantially uniform temperature of the atmosphere which enters a minimum relative himidity throughout the drying period for all of the stock loads, and of replacing each row when it is dry with a green row.

8. The method of drying which consists of serially charging into an enclosure a series of rows of air permeable stock loads of material to be dried in spaced relationship, one row at a time at substantially regular time intervals so loads has been dried a that each row of stock difierent amount from the other rows, of recirculating a drying atmosphere across all the rows of loads, of venting a portion of the circulating atmosphere and replacing it with fresh the common atmosphere as it passes from one row of loads to anotherin recirculation form temperature of the atmosphere which ento maintain a substantially uni-,

at substantially regular time intervals so that ters a stock load, and of replacing each row when it is dry with'a green row.

9. The method of drying which consists of serially charging into an enclosure a series of rows of air permeablestock loads of material to be dried in spaced relationship, one row at a time each row of stock loads has been dried a different amount from the other rows, of recirculating a drying atmosphere across all the rows of loads, of venting a portion of the circulating atmosphere and replacing it with fresh air, of conditioning the common atmosphere as it passes from one row of loads to another in recirculation to maintain a substantially uniform temperature of the atmosphere which enters a stock load, of reversing the direction I of the circulation across the series of loads at will, and of replacing each row when it is dry with'a green row.

' JAMES FORREST coma. 

